An electric generator comprising a rotor having a magnet such as a permanent magnet and a stator having a coil may be improved in power generation efficiency as the number of turns of the coil is large. However, increasing of the number of turns of the coil enlarges size of the electrostatic generator.
On the other hand, JP 2006-340425 A, for example, discloses a motor reduced in size and improved in output by arranging the magnet of the rotor side and the coil of the stator side in a predetermined positional relationship. Therefore, it is considered to obtain an electric generator with high power generation efficiency by adopting the positional relationship between the magnet and coil of such a motor.
Further, in the electric generator as described above, it is known that when the rotor rotates cogging torque is generated in relation to the core. Such cogging torque is caused by attractive force or repulsive force generated between the magnetic poles of the rotor and the core and would cause cogging on rotation of the rotor. Therefore, the rotation of the rotor becomes unstable by the cogging torque. Regarding such a point, JP 2006-101695 A, for example, discloses a mean for suppressing cogging by making the shape of the part for mounting the magnet of the rotor into a predetermined shape to moderate the change in magnetic flux at the rotor rotating.